According to Flurry, the U.S. share of Android and iOS app sessions shrank a remarkable 19 percentage points in the past year. U.S.-based sessions now account for less than one-third of the total. The next nine largest markets soaked up much of the usage, increasing their share 12 percentage points to 39 percent of app sessions.

While the U.S. is still the most profitable market for app makers, developers need to start turning their eyes toward the global market, where much of the growth in mobile apps will occur as smartphone penetration slows in the U.S. and other early adopter markets.